This invention relates to a device and method to establish communication through an interface between a subscriber unit and a Local Exchange on a telecommunication line intended for digital traffic, for instance an ISDN access.
In general, telephones are connected via an analogue telephone line for speech transmission through PSTN (PSTN=Public Switched Telephone Network) to a local exchange (LE). To enable transmission of digital data, e.g. from a personal computer, a modem, which converts digital data to analogue signals, is inserted between the computer and the telephone line. If subscribers want to connect to for instance INTERNET, the LE must have one modem per subscriber call, for connection to ISDN (Integrated Services Digital Network). The use of modems also makes digital transmissions rather slow, about 28 kbit/s, and this is a drawback, particularly since the use of computers and terminals in households and companies has been increased and thus also the need for digital transmissions with higher bit rate.
Thus, it has become more interesting to use the ISDN access for the subscriber PSTN service even for household telecommunication traffic, since then digital communication rate for digital communication could be increased, to about 128 kbit/s, in relation to digital communication on analogue telecomunication lines.
A possibility used for transmission of digital data as well as speech across the telephone network, is ISDN-BA (Integrated Services Digital Networkxe2x80x94Basic Access). The transmission could then go directly from a subscriber station to an LE. In the prior art the subscriber has been provided with a Network Termination (NT) terminating the transmission towards the LE. Terminal Equipment TE, such as computers or other kinds of terminal equipment, are connected directly to the NT, while telephones are connected via an A/D- and D/A-converter equipment (TA) for speech transmission to and from the NT.
Since the NT analogue/digital and digital/analogue convert the speech transmission from and to the telephone set in order to adapt it to be transmitted across the ISDN line between the NT and the LE, problems arise regarding particular features which can be used in transmission via the PSTN. Thus, PSTN signalling from the analogue interface was mapped to ISDN across the standard ISDN-BA. By doing this mapping the call from PSTN will be recognized in the LE as ISDN. This results in limitations of services for the existing PSTN. For example, it is not possible to subscribe to services like Calling Line Identity (CLI) or the like.
Another drawback with the prior use of ISDN-BA for telephone communications is the need for two additional units at the subscriber station, the NT and the TA.
An interface to an ISDN-line for analogue telephones and computers is described in U.S. Pat. No. 5,305,312. A processor having a stored program controls access to the ISDN-line for the analogue and digital interface circuits. The telephones with their analogue interface and the computers with their digital interface are connected in parallel to an ISDN bus. The processor provides access to switch-controlled ISDN features for the analogue telephones, such as call waiting etc, i.e. the selfevident call control information features which always have to be there. However, more sophisticated, modern services, such as CLI, are not supported by the device and method described in the U.S. Pat. No. 5,305,312, and this depends upon that only a mapping is provided in the subscriber station for transferring the analogue signalling of the telephone set to be adapted for ISDN signalling, just as in the prior art using the TA equipment described above.
It is an object of the present invention to provide a method and a device for enabling a subscriber to keep the same services for speech transmissions as can be provided for PSTN when upgrading from PSTN to ISDN-BA.
Another object of the invention is to provide a method and a device having the need for only one additional unit at the subscriber station.
Still another object of the invention is to provide a method and a device in which the B-channels between the subscriber station and the network to which it is connected could be chosen arbitrary and not dependent upon if the transmission is a speech or a data transmission.
These objects are achieved by a method having the features in claim 1, and a device for performing the method is disclosed in claim 6. Further features and improvements of the invention, are disclosed in the dependent claims.
The invention provides a method and an equipment to establish communication through an interface between a subscriber unit and a Local Exchange on a telecommunication line intended for digital traffic, for instance an ISDN-line. Packages are transmitted according to a protocol comprising PSTN speech communication together with at least service functions for telephone communication between the subscriber unit and the Local Exchange. An amended protocol could be used for this protocol of a kind ordinarily making PSTN speech communication through an inter-Face between an Access Network and a Local Exchange. A part, e.g. an address field, of the protocol could allocate a B-channel for communication to a particular call arbitrary at a call set-up. The protocol could support communication between an access connected to a telephone set in the subscriber unit and a call control in the Local Exchange. Preference procedure operations for allocating available B-channels to subscriber calls could be written into the protocol. The protocol could support digital IP-packets to be sent down on all available B-channels on demand. The protocol could also disconnect an occupied B-channel for a new call if more than one B-channel is occupied by the same traffic service or if the new call has a higher priority than the call occupying the B-channel.
The European Telecommunications Standard Institute (ETSI) has produced standards of type V, for instance the V5.1 interface (ETS 300 324-1), as an interface between two systems, an Access Network (AN) and a Local Exchange (LE), with flexible (provisioned) information B-channel (bearer channel) allocation. Supported access types in the V5 interface standard are ISDN-BA and PSTN services. ISDN-BA are provided for digital communication and PSTN for speech communication.
However, the standard does not yet comprise a mixture of PSTN and ISDN-BA across the same access digital section, for instance ISDN-BA, and this is of interest for the present invention. A part of this standard interface, i.e. ETS 300 324-1:1994, clause 13, with some amendments can be used as a protocol between a subscriber station and a LE. Thus the invention provides a method and a device in which the PSTN signalling priciples of the V5.1 interface standard (ETS 300 324-1, particularly clause 13) can be amended for use even for other kinds of communications than between an AN and a LE, and in particular to mix PSTN and ISDN-BA traffic on the same traffic line.
PSTN is unique in every country in Europe, and also in other countries. The V5.1 standard has defined the protocol stated above to transfer analogue line signalling between a PSTN terminal and the LE traffic handling functions (call control).
However, the standard does not describe how to choose B-channels for PSTN, since it has not earlier been possible to choose them, i.e. PSTN has always had a fixed allocated 64 kbit/s B-channel. If there are two B-channels in a mixed line for PSTN and ISDN-BA across the same access, both B-channels were owned by the ISDN-BA traffic.
The invention provides a way to overcome this drawback by providing a particular protocol in a network termination unit, also called NTN, in the subscriber station and also in the LE regarding the particular subscriber station which protocol for the PSTN traffic transmits packages between these devices comprising PSTN speech communication together with wanted service functions across the ISDN-BA line. The protocol could also let the LE allocate a B-channel arbitrary among the B-channels in the traffic line between the two devices.
Thus, the protocol comprises features to communicate across the D-channel from the LE to the subscriber equipment the B-channel which is choosen for an actual traffic PSTN communication. The programming for providing this is obvious for a person skilled in the art and is therefore not described here.
It is convenient to use an existing standard as far as possible and thus to make use the mechanisms already defined there. Since only one subscriber telephone set, or a very limited number of subscriber telephone sets, is connected to the network termination unit at the subscriber station the L3addr in the V5.1 protocol mentioned above will be useless for its intended purpose of controling traffic to different logical user ports in an Access Network. Thus the L3addr could be used for other purposes.
However, it is also within the scope of the invention to use another kind of protocol providing the same service and service functions disclosed above between the LE and the subscriber station and also to make use of and make some amendments on other standard protocols as well, such as the BCC protocol defined in V5.2 (ETS 300 347-1, clause 17).
According to an aspect of the invention this part of the standard protocol is used for a subscriber wanting to have a limited number of B-channels and thus more bandwidth for different services. This part of the protocol is then used for allocating an arbitrary B-channel for whichever service to be provided at the moment being and to communicate the kind of service and service functions and the B-channel in question across the D-channel. This part of the protocol could also be provided with priority and preferance features in order to allocate one or more B-channels to particular data services in dependence of the momentary level of traffic on the B-channels. An advantage of using an already existing protocol is that relevant parts of it could be reused for writing wanted specifications for the client. However, the protocol mentioned above in V5.1 is the preferred one, since it demands a reasonable computer utility, and thus represents the cheapest way for the inventive application.
Sometimes an AN could be coupled between the subscriber station and the LE. This AN will then be transparent for the signalling procedures between the LE and the subscriber station.
The advantage with the invention is that both rapid digital communication and speech communication keeping the same services as before when upgrading from PSTN to ISDN-BA could be provided. Also, communication with common information networks, such as INTERNET, could be done at a high rate.
The invention will provide a customer station with both an ISDN basic access User Network interface with access to the ISDN services and a PSTN interface with full access to the PSTN services.